1. Field of the Invention
This invention relates to a video signal noise reduction apparatus, a method of reducing a noise in a video signal, and a recording medium storing a program of the method.
2. Description of the Prior Art
A video signal noise reduction apparatus for reducing noise in a video signal by averaging the video signal in accordance with a correlation result between the center and peripheral pixels are known.
Japanese patent application provisional publication No. 6-86104 discloses such a prior art video signal noise reduction apparatus.
FIG. 6 is a block diagram of the prior art video signal noise reduction apparatus disclosed in this Japanese patent provisional application.
A video signal from an input terminal 501 is supplied to a center and peripheral pixel data output circuit 502. The center and peripheral pixel data output circuit 502 supplies center pixel data and peripheral pixel data to absolute value circuits 503 to 506. The absolute value circuits 503 to 506 calculate difference in values of the peripheral pixels from that of the center pixel and operates absolute values which are supplied to a correlation judging circuits 507 to 510. The correlation judging circuits 507 to 510 compare the absolute values from the absolute value circuits 503 to 506 with a threshold value to judge the presence or the absence of correlation. The judging results are supplied to counter 511 and to correlation pixel adder 512. The counter 511 counts the number of the pixels showing correlation and the count is supplied to a divider 513.
The correlation pixel adder 512 obtains a sum of values of only pixels showing correlation. The sum is supplied to the divider 513. The divider 513 divides the sum from the correlation pixel adder 512 by the count from the counter 511 and the dividing result is outputted as the output video signal. Thus, the dividing result replaces the value of the center pixel, so that the video signal is averaged to reduce noise in the video signal.
The divider makes the circuit scale large.
The aim of the present invention is to provide a superior video signal noise reduction apparatus, a superior method of reducing a noise in a video signal, and a superior recording medium storing a program of the method.
According to the present invention there is provided a video signal noise reduction apparatus. A pixel data outputting circuit responsive to a pixel clock signal outputs data of a center pixel and data of peripheral pixels from a video signal. A difference calculation circuit calculates differences of the data of the peripheral pixels from the data of the center pixel. A correlation pixel data detecting circuit detects a portion of the data of the peripheral pixels showing high correlation with the data of the center pixel in accordance with the differences and a threshold value. A counting circuit counts the portion of the data of the peripheral pixels from the correlation pixel data detecting circuit. A correlation pixel selecting circuit responsive to the correlation pixel data detecting circuit selectively outputs a portion of the differences of the portion of the data of the peripheral pixels. A summing circuit obtains a sum of the portion of the differences in accordance with the counting result. A dividing coefficient generating circuit generates a dividing coefficient of 2n in accordance with the counting result of the counting circuit. A dividing circuit divides the sum with the dividing coefficient. An adding circuit adds the dividing result to the center pixel data to generate an output video signal.
In the video signal noise reduction apparatus, the summing circuit includes a weighting circuit which weights each of the portion of differences in accordance with a predetermined priority, the summing circuit obtains the sum from the weighted differences.
According to the present invention there is also provided a method of reducing noise in a video signal including the steps of: outputting data of a center pixel and data of peripheral pixels from a video signal in response to a pixel clock signal; calculating differences of the data of the peripheral pixels from the data of the center pixel; detecting a portion of the data of the peripheral pixel showing high correlation with the data of the center pixel in accordance with the differences and a threshold value; counting the detected portion of the data of the peripheral pixels; selectively outputting the detected portion of the differences of the portion of the data of the peripheral pixels; obtaining a sum of the portion of the differences in accordance with the counting result; generating a dividing coefficient of 2n in accordance with the counting result; dividing the sum with the dividing coefficient; and adding the dividing result to the data of the center pixel to generate an output video signal.
The method of reducing noise further includes the step of weighting each of the portion of differences in accordance with a predetermined priority. The sum is obtained from the weighted differences.
According to the present invention there is further provided a recording medium comprising; a base; and a recording layer storing a program including the steps of: outputting data of a center pixel and data of peripheral pixels from a video signal in response to a pixel clock signal; calculating differences of the data of said peripheral pixels from the data of the center pixel; detecting a portion of the data of the peripheral pixels showing high correlation with the data of the center pixel in accordance with the differences and a threshold value; counting the detected portion of the data of the peripheral pixels; selectively outputting the detected portion of the differences of the portion of the data of the peripheral pixels; obtaining a sum of the portion of the differences in accordance with the counting result; generating a dividing coefficient of 2n in accordance with the counting result; dividing the sum with the dividing coefficient; and adding the dividing result to the data of the center pixel to generate an output video signal.
The program further includes the step of weighting each of the portion of differences in accordance with a predetermined priority. The sum is obtained from the weighted differences.